About this replacement
Apple MacBook Pro 15" Unibody 2009 — 10.95V Li-Polymer Replacement Battery (A1321)
This is a 10.95V, 7200mAh Li-Polymer battery for the Apple MacBook Pro 15 inch Precision Aluminum Unibody 2009 models, including the A1286 chassis and MC118LL/A SKU. It fits the 15.4" 2.53GHz Core 2 Duo configuration and replaces OEM part numbers A1321, 661-5211, 020-6380-A, and 661-5476. Capacity on this cell matches the original spec at 78.84Wh.
- A1286 chassis compatibility: All 2009 MBP 15" Unibody variants share the same six-cell Li-Polymer stack, battery connector pinout, and SMBus communication line — the same physical cell and BMS handshake covers the full model range listed here.
- Bench tested on actual hardware: We ran this cell on an A1286 board. The SMBus negotiation completed without fault codes, the BMS reported correct voltage at each charge threshold, and the charging circuit stepped through trickle, CC, and CV phases without interruption.
- Post-install calibration on the 2009 MBP: After fitting this cell, run the laptop on battery until it reaches hibernate cutoff, then charge uninterrupted to 100% without sleep. This resets the SMBus fuel gauge IC learn cycle against the new cell and clears the "Replace Now" health warning that macOS displays after every cell swap.
Why the A1286 shuts down at 20–30% after a battery swap
The 2009 MBP uses a Texas Instruments fuel gauge IC that stores learned discharge curves from the previous cell in non-volatile memory. When a new cell goes in, that stored curve no longer matches the actual chemistry — so the IC predicts empty far too early. Under combined CPU and display load, the board sees a voltage dip the IC interprets as cutoff and kills power. Running one full discharge-to-hibernate then a complete uninterrupted charge forces the IC to rebuild its curve against the new cell's actual voltage profile.
macOS showing 0% or "Service Battery" immediately after fitting a new cell
This happens because the EEPROM on the old battery held cycle count and health data that macOS cached. The new cell arrives with a different EEPROM state, and macOS briefly reports an unknown or degraded battery until the SMBus syncs. Reset the System Management Controller by shutting down, holding Shift+Control+Option+Power for ten seconds, then booting. After one full calibration cycle the health status normalises and the Wh figure in System Information aligns with the 78.84Wh rated capacity of this cell.